Traditionally bullets for small arms ammunition have been manufactured from lead and lead alloys. The major advantages of lead as a bullet material are its relatively low cost, high density and high ductility. The high density of lead has been particularly important to bullet design because the energy generated by the weight of a bullet is critical to the proper functioning of modern semi-automatic and automatic weapons, the in-flight stability of the round, and the terminal effects of the bullet.
The highly toxic nature of lead, however, and its propensity to fume and generate airborne particulate, place the shooter at an extreme health risk. The more a range is used, the more lead residue builds up, and the greater the resulting lead fume and lead dust pollution (particularly for indoor ranges). Moreover, the lead bullet residue left in the earthen berm of outdoor ranges can leach into the soil and contaminate water tables. In order for indoor ranges to operate safely, they require extensive and expensive air filtration systems, and both indoor and outdoor ranges require constant de-leading. These clean up operations are time consuming, costly and repetitive. Accordingly, there is a great need for lead-free bullets.
Additionally, personnel at range operations are concerned with the ricochet potential and the likelihood of causing "back-splatter" of the training ammunition. Back-splatter is a descriptive term for the bullet debris that bounces back in the direction of the shooter after a bullet impacts on a hard surface, such as steel targets or backstops. Ricochets present a significant hazard to individuals, equipment and structures in and around live firing ranges. A ricochet can be caused by a glancing impact by a bullet on almost any medium. Back-splatter presents a significant danger to shooters, training personnel standing on or around the firing line and observers. When a bullet strikes a hard surface at or near right angles, the bullet will either break apart or deform. There is still energy in the bullet mass, however, and that mass and its energy must go somewhere. Since the target material or backstop is impenetrable, the mass bounces back in the direction of the shooter.
It is believed that a key way to minimizing the risk of both ricochet and back-splatter is to maximize the frangibility of the bullet. By designing the bullet to fracture into small pieces, one reduces the mass of each fragment, in turn reducing the overall destructive energy remaining in the fragments.
Several prior art patents disclose materials and methods for making non-toxic or frangible bullets or projectiles. For example, U.S. Pat. No. 5,442,989 to Anderson discloses projectiles wherein the casing is frangible and made out of molded stainless steel powder or a stainless steel+pure iron powder mix with up to 2% by weight of graphite. The casing encloses a penetrator rod made of a hard material such as tungsten or tungsten carbide. This projectile is mainly for 20-35 mm cannons to engage targets such as armored vehicles, trucks, buildings, ships, etc. Upon impact against the target, the casing produces fragments which are thrown in all directions with great energy while the penetrator rod pierces the target.
U.S. Pat. No. 4,165,692 to Dufort discloses a projectile with a brittle sintered metal casing having a hollow interior chamber defined by a tapering helix with sharp edge stress risers which provide fault lines and cause the projectile to break up into fragments upon impact against a hard surface. The casing is made of pressed iron powder which is then sintered. This projectile is also designed for large caliber rounds such as 20 mm cannon shots.
U.S. Pat. No. 5,399,187 to Mravic et. al. discloses a lead-free bullet which comprises sintered composite having one or more high density powders selected from tungsten, tungsten carbide, ferrotungsten, etc., and a lower density constituent selected from tin, zinc, iron, copper or a plastic matrix material. These composite powders are pressed and sintered. The high density constituent allows bullet densities approaching 9 g/cm.sup.3.
U.S. Pat. No. 5,078,054 to Sankaranarayanan et. al. discloses a frangible projectile comprising a body formed from iron powder with 2 to 5% by weight of graphite or iron with 3 to 7% by weight of Al.sub.2 O.sub.3. The powders are compacted by cold pressing in a die or isostatic pressing, and then sintered.
U.S. Pat. No. 5,237,930 to Belanger et. al. discloses a frangible practice ammunition comprising compacted mixture of fine copper powder and a thermoplastic resin selected from nylon 11 and nylon 12. The copper content is up to about 93% by weight. The bullets are made by injection molding and are limited to densities of about 5.7 g/cm.sup.3. A typical 9 mm bullet only weighs about 85 grains.
None of the above discussed patents disclose or suggest lead-free, frangible bullets made of predominately copper with densities approaching that of conventional bullets. An objective of this invention is to provide a range of lead-free frangible bullets, optimized for frangibility, which will eliminate the lead fumes and dust hazard to the shooter while also minimizing the ricochet and back-splatter hazards. A further objective is to provide a low cost material and process for making such a bullet. Yet another objective is to provide a bullet with a weight (hence density) as high and as close to the conventional lead bullet as possible so that the recoil and the firing characteristics closely resemble those of conventional lead bullets. Yet another objective is to reduce the risk of lead residues leaching into the soil and water table in and around shooting ranges.